The invention relates to methods and apparatus for producing a combustible fuel, torrefaction of biomass, producing carbon dioxide offsets as well as an article of manufacture. Carbon-offset programs are the latest rage. Various entities have promised to mitigate greenhouse gas emissions from diverse activities. Europe established a cap-and-trade system last year that limits carbon dioxide emissions from about 50 percent of industry to reach its emissions goals as dictated by the Kyoto Protocol. Officials modeled the system on the sulfur dioxide trading market established in the U.S. in 1995, which has successfully cut levels of acid rain. As the trading market evolves, some environmentalists think that voluntary offset programs could join existing cap-and-trade market schemes to cut emissions even more substantially.
The need for an immediate solution to replace our depleting and air polluting fossil fuel energy sources is of the utmost importance. The increase in the use of non-renewable coal and oil requires an immediate replacement fuel to prevent severe economic, health and social problems. One solution is renewable solar energy that replaces the use of coal in electric power generating plants. This approach has not been widely utilized.
Fossil Fuel use for electric power plants, heat energy and transportation is continuing to increase at an alarming rate. Coal fired power plants use most of the coal and produce most of the fossil fuel air pollution. For each ton of carbon burned, 3.67 tons of carbon dioxide is generated. The global use of carbon emissions are over 7 billion tons per year and is expected to reach 14 billion tons per year by 2050.
The concentration of carbon dioxide in our atmosphere has increased over 35% since the late 18th century. The level is now at 379 parts per million by volume and climbing. Estimated increases in the last year are alarming.
Many scientists believe that it will take a joint effort in many areas with many new, yet to be invented, technologies to simply hold the concentration of carbon dioxide to present levels. One recent example of some ideas was recently presented by industry and governments on Global Warming. These include these 7 steps (New York Times Nov. 30, 2006)
1. New inventions that can capture 90% of the carbon dioxide from 800 new billion-watt coal-burning power plants.
2. Build 880 new nuclear power plants in lieu of new coal power plants.
3. Increase auto efficiency for 2 billion cars from 30 to 60 miles per gallon.
4. Increase the use of wind power 80 fold and use that energy to make hydrogen fuel for cars.
5. Raise the efficiency of 1,600 full size power plants, that utilize energy locked in coal, from 40 to 60%.
6. Conservation—Cut 25% of electricity use in homes, offices and stores.
7. Increase solar generated electricity by 700 fold.
These are worthwhile goals, however, the cost to implement these technologies would be staggering and some of these technologies create new problems. The ultimate solution requires innovative technologies. Many scientists say the only real long term prospect for significantly substituting for fossil fuels is a breakthrough in harvesting solar power.
Fossil fuels with their very high carbon content, are the predominate fuels today. They have been relatively easy to extract from the earth and to use with minimum processing and have a high heat content. It has only been in recent years has the negative impact of using this “Non-Renewable Fossil Fuel” on such a large scale that the negative impact to our environment has been fully recognized. In addition, fossil fuels are being depleted at an alarming rate and alternative energy resources must be found to fuel the world. Throughout the world all nations are facing the challenge of developing clean solar “Renewable Energy Fuels” to replace coal and other fossil fuels. Nuclear and other promising energy sources are at best many decades away from being practical on a large scale basis.
Carbonized wood and charcoal have long been known as high quality fuels that produce high energy and little smoke, however, they are costly to produce. Wood has returned as one of the fuels of choice out of necessity, but its moisture content along with the smoke and volatile organic compounds given off during burning have limited its use. With the necessary increase in the use of wood even with its air pollution burning problems, it is being used more and more today. Collecting and transporting wood having a low density such as 10 to 15 pounds per cubic foot has been solved with newer and better technologies that include chipping, shredding, milling and pelletizing where the wood is converted into practical pellet forms with a density of 40 plus pounds per cubic foot. This has opened new opportunities to further improve the burning properties of wood as a more practical replacement for fossil fuel.
Over the last 25 years an improved fuel source using wood that has been heated in the absence of oxygen has received considerable attention. This treated wood is called torrefied wood (TW). Numerous attempts have been made to produce this high energy, low pollution fuel with very limited success. Even with all the various methods considered, none has been practical. Even though coal fired electric power plants have found that using some torrefied wood mixed with coal greatly reduces the air pollution generated, the high cost of producing consistent quality torrefied wood simply does not exist with all prior art methods of production.
Wood has been used as a fuel for thousands of years. Wet wood may contain over 50% water. When burned, incomplete combustion occurs and it uses most of its energy to turn the water into steam and produces considerable smoke and thousands of forms of noxious gasses. Dry wood, as used in many fireplaces, may contain approximately 22 percent moisture. For any specific wood being burned, the dryer the wood being burned, the more complete the combustion. Dry wood burns cleaner than wet wood, but incomplete combustion still occurs, resulting in the formation of carbon monoxide and many volatile organic compounds and other undesirable air polluting gases. The pollution levels produced are unacceptable for most air pollution agencies. Some agencies are banning wood burning but accepting the use of wood pellets in special heaters because wood pellets typically contain less moisture (approximately 10%). However, a substantial amount of volatile organic compounds still exists in very dry wood. When wood pellets formed from dry wood are burned they can generate nitrogen oxides and other greenhouse gases and smog.
Carbonized wood is a three thousand year old technology that has been looked at to help replace coal. However, the process is inefficient because, in part, it consumes too much energy. A very promising improvement in technology was developed in the 1980's by the French when they commercially converted wood into torrefied wood. Torrefied wood has the moisture and most volatile organic compounds (VOC's) driven out resulting in a high percentage of carbon content. In addition, the chemistry and structure of the wood itself is converted into a new form by continued exposure to heat. The French process used heat treatment by an inert gas to drive out the unwanted moisture and volatile organic compounds and stopped the process before it became carbonized. The torrefied wood burned clean but production costs were high along with a complex system with high potential for fires that prevented this from practical commercial use.
Several inventions since have tried to perfect and improve the torrefaction process by using high pressure steam, high temperature inert gas, superheated steam and other gas, pressure and vacuum methods. Some of these technologies claimed to improve efficiencies but all have failed to overcome the practical conversion of wood into torrefied wood in a simple, easy, quick, practical, safe, uniform and economic way. What these prior technologies accomplished was demonstration projects that showed how using torrefied wood in co-firing with coal could result in cleaner burning with less air pollution generated. Again, all prior art methods have been too complex, too expensive, and have not been practical for commercial use.
A number of prior art methods exist for producing torrefied wood. These methods all use inert gas, high pressure steam, or superheated steam in the heat treatment process. These prior art methods primarily use convection heat transfer between the wood surface and the heat source such as a steam or inert gas medium. Using any type of inert gas or steam involves large containment systems with large amounts of surface area, high equipment costs, high energy costs, slow treatment rates, and low overall operating efficiencies with resultant high production costs. Maintaining an oxygen free inert gas environment to these systems adds to the complexity and costs.
With all these prior art methods the systems and equipment has to be complex and large to contain the inert gas or stream heat transfer medium. The high operating pressures required with steam, sometimes over 600 psi, require heavyweight materials for construction of the equipment utilized and typically utilize batch processes rather than continuous processes. These convection batch systems are inefficient and costly to perform, thus, the final product produced by such convection systems is expensive.
The torrefied wood produced in all prior art methods does not contain the heat transfer fluid (HTF) of this invention. Thus, the heat content is less at about 8,000 to 9,000 Btu per pound.
Even though torrefied wood works extremely well, as a fuel in co-firing with coal to reduce pollution, very little has been produced due to the overall processing inefficiencies and high costs of all prior art systems.